1. Field of the Invention
The present invention relates to a single point bonding method in which leads connected to pad (electrodes) of a chip (semiconductor elements) are individually connected to pads on a circuit board or in which leads of chips are individually connected to pads of chips.
2. Prior Art
The packaging of semiconductor elements is accomplished, for example, in the following manner:
As shown in FIG. 5(a), leads 2 of a chip 1 are connected to the pads 4 of a chip 3, the leads 2 are cut to a prescribed length, and then each lead 2 is formed into a stress-absorbing shape. As shown in FIG. 5b, the respective leads 2 attached to the chips 3 are individually connected to corresponding pads 6 of a circuit board 5 by a bonder using heat-and-pressure bonding in combination with ultrasonic waves.
The shaping of the leads 2 as referred to above is done in order to absorb the stress which is caused by the difference in thermal expansion between the chip 3 and the circuit board 5 and also in order to alleviate the stress occurring during electrical testing and packaging. Packaging configurations of this type are described on page 215-223 of "TAB Gijutsu Nyumon [Introduction to TAB Techniques]" written by Kenzo Hatada and issued by Kogyo Chosakai. In addition, a single point bonding method in which respective leads are individually connected to respective pads is described in, for example, Japanese Patent Application Laid-Open (Kokai) No. 2-299247.
In the prior art described above, it is necessary to use a shaping die for accomplishing the shaping of the leads 2, which increases equipment expenditures and the number of processes required in semiconductor assembling, resulting in increased cost. Furthermore, in the conventional single point bonding method described above, the leads 2 are merely bonded by applying ultrasonic waves thereto with a load being applied to the leads 2 by way of lowering a bonding tool to press each lead 2 against the corresponding pad 6. In this method, therefore, the leads 2 are not formed into a shape that can absorb the stress.